Pneumatic control circuits have been utilized in a number of different employments. One such employment is a tool for applying a tensioned strap to an article. The general construction and operation of these strapping tools is evident, for example, from the following United States Patents:
______________________________________ Kobiella 3,442,203 05/06/69 Ericsson 3,586,572 06/22/71 Frey 3,679,519 07/25/72 Wedeking et al. 4,305,774 12/15/81 Becking 4,629,530 12/16/86 Cearlock et al. 4,657,626 04/14/87 ______________________________________
Generally, these tools apply a strap, usually supplied on a stock spool of sorts, around an outer periphery of an article, such as a box and the like. The strap, which can be of various constructions, such as high strength polyester, and the like, is tensioned around the article, and opposite ends of the strap are then welded or otherwise joined together to form a continuous loop around the article. By welding the opposite ends of the strap together, a clip need not be used to join the opposing ends of the strap to complete the loop, resulting in increased cost savings to the operator because such clips do not need to be purchased.
Particularly illustrative of these tools are the VFL and VFM TENSION-WELD.TM. strapping tools provided by the Signode Corporation. The VFL and VFM tools are illustrated and described in detail in the Signode Corporation's "Operation, Parts and Safety Manual" number 186096. These tools are provided with means for automatically tensioning the strap around the article.
However, with these tools, the operator is required to use his own judgment to determine appropriate temporal durations of the welding process for joining opposing ends of the strap, and of appropriate cool down times for insuring that the weld joining the opposite ends of the strap has sufficient structural integrity to remain tensioned around the article without rupturing. Because each operator's judgment is subjectively different, the tension and structural integrity of the straps can vary from article to article. The strap may not be properly tensioned or strong, possibly resulting in damage to the article. Accordingly, it is desirable to automatically and objectively determine the duration of the welding process.
Appropriate tools have been constructed which can automatically determine the duration of the welding process. The VXL-2000 and VXM-2000 TENSION-WELD.TM. strapping tools, illustrated and described in detail in the Signode Corporation's "Operation, Parts and Safety Manual" number 286102, are examples of tools having means for automatically determining duration of the welding process in the form of a time control circuit. The particular construction of this time control circuit is the subject of the co-pending U.S. patent application of Toppel, Ser. No. 07/476,873, filed on Feb. 8, 1990, now U.S. Pat. No. 5,169,480. That co-pending application is assigned to the assignee of the present invention, and the disclosure thereof is incorporated herein by reference.
The VXL-2000 and the VXM-2000, as well as the device and circuit disclosed in the above-referenced co-pending application, represent a second, improved generation embodiment of the VFL and the VFM TENSION-WELD.TM. strapping tools. However, both the original and second generation of those tools require an operator to use his judgment to determine the appropriate cool down time for the weld. If the weld applied between the opposing ends of the strap is not allowed to cool sufficiently, then the structural integrity of the resulting loop may be compromised by failure of the weld. This can result in damage to the article. Also, if the weld has not been properly cooled, the resulting loop may not be tensioned around the article as desired. Accordingly, it is desired to objectively and automatically determine the cool down time for insuring the structural integrity of the weld, as well as the resulting loop.
The present invention is intended to solve some, if not all, of the problems presented by the hand strapping tools of the prior art.